OBJECTIVE: The principal aims of this project are characterization of viral and host genes involved with neoplastic transformation by RNA tumor viruses and cellular regulation of these agents at the molecular level. The specific experiments currently undertaken include the development of a technique for describing the organization of sequences in viral genomic RNA. Attention is focused on sequences which differ from those of non-oncogenic endogenous viruses, and which are newly inserted into the genome of infected and transformed cells. These include sequences which differ in viruses which vary in their oncogenic properties (that is, cause different types of tumors) and in their susceptibility to regulation by the host cell. APPROACH: These studies are carried out with genomic RNA from cloned, highly purified viruses from the avian leukosis-sarcoma complex and DNA from either infected tissue culture cells and tumors or from normal chick embryos. The principal technique used is hybridization of viral RNA, and specific fragments of viral RNA, with DNA from either infected or normal cells. This is carried out in either the presence or absence of competitor RNA from various sources. The presence of viral sequences found only in infected tumor cells of various type and their location in viral RNA as well as their presence or absences in different viruses can be determined in this fashion.